In a known method for producing amino acid using an enzyme, a 5-substituted hydantoin compound synthesized chemically at a low cost is employed as a starting material and is decomposed asymmetrically into optically active amino acids. A method for producing optically active amino acid from such a 5-substituted hydantoin compound is important for producing pharmaceuticals, chemical industrial products, food additives and the like.
In a method for producing optically active amino acid from such a 5-substituted hydantoin compound, the following enzymes (1) and (2) are required:
(1) An enzyme which catalyzes an N-carbamylamino acid producing reaction via an action on a 5-hydantoin compound to hydrolyze this compound: hydantoin hydrolase (hydantoinase).
(2) An enzyme which catalyzes an optically active amino acid producing reaction via an action on a resultant N-carbamylamino acid to hydrolyze this compound, N-carbamylamino acid hydrolase (carbamylase).
For producing optically active amino acid from a 5-substituted hydantoin compound describe above, an enzyme which is optically selective for at least one of (1) hydantoinase and (2) carbamylase may be employed, and known methods employ a microbial enzyme system or a microbial enzyme system combined with a chemical reaction system.
Among such known methods, a known method for producing D-amino acid from a 5-substituted hydantoin compound using a D-amino acid producing microorganism or a material containing an enzyme produced by the microorganism employs a Pseudomonas microorganism (Japanese Patent Application Publication No. 56-003034) or an Agrobacterium microorganism (Japanese Patent Application Laid-open No. 019696). Such a D-amino acid producing microorganism frequently has a hydantoinase activity specific generally to a 5-substituted hydantoin in a D form, and when using a DL-5-substituted hydantoin (5-benzylhydatoin as an example here) as a starting material, the D form is hydrolyzed exclusively to form an N-carbamyl-D-amino acid, which is then hydrolyzed by a D-carbamylase which acts exclusively on the D form, resulting in only an amino acid in the D form (D-phenylalanine as an example here), as shown in the following scheme.
